1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods and apparatus for cables for high speed data communications.
2. Description of Related Art
High speed data communications over shielded cables are an important component to large high-end servers and digital communications systems. While optical cables provide long distance drive capability, copper cables are typically preferred in environments that require a shorter distance cable due to a significant cost savings opportunity. A typical copper cable used in environments requiring a shorter distance cable, is a twinaxial cable. A twinaxial cable is a coaxial cable that includes two insulated, inner conductors and a shield wrapped around the insulated inner conductors. Twinaxial cables are used for half-duplex, balanced transmission, high-speed data communications. In current art however, twinaxial cables used in data communications environments are limited in performance due to a bandstop effect. That is, typical twinaxial cables for high speed data communications have certain drawbacks. Typical twinaxial cables have a bandstop filter created by overlapped wraps of a shield that attenuates signals at frequencies in a stopband. The attenuation of the signal increases as the length of the cable increases. The attenuation limits data communications at frequencies in the stopband.
Signal attenuation is becoming more and more important with the ever increasing need for high-speed transmission. Signal attenuation in cables can result from number of factors such as dielectric loss, skin effect, conductor loss, and radiation. In high-speed shielded cables, skin effect is a major contributor for attenuation at high frequencies. The results of skin effect at high frequency can be predicted, but the loss due to improper current return path is a major bottle neck in high speed shielded cables. In twinaxial cable, a wrapped foil shield typically provides a current return path for a high speed, alternating current signal, and there is a current return path discontinuity at every overlap of the shielding foil. Each such discontinuity contributes to an overall impedance mismatch and signal loss.